A conventional focusing way of the microscope is a manual way. This focusing way is dependent on subjective judgment completely, which results in a poor focusing efficiency. Especially, when there are a large amount of objects, it can cause visual fatigue of the operator easily. This reduces focusing precision for the objects and causes tired feeling for the operator.
Most of related auto-focusing microscopes control the stage or the main body of the microscope to move to search a preset object distance, thereby achieving auto-focus, as shown in FIG. 1. Adjustable range of this method is limited and when the object is big, support for the microscope needs to be very long to achieve proper focusing. This is inconvenient for manual observation and use.
A work distance of a conventional microscope is usually fixed because the image distance of the conventional microscope is fixed and the magnification of the objective lens is also fixed. It can be learned from the optical system that when the magnification and the image distance are fixed, the object distance is also fixed, i.e., the work distance is fixed. The stage of the conventional microscope moves according to different objects to find the object distance for clear imaging and correct focusing. The fixed work distance would cause that when the object is high, the microscope cannot achieve correct focusing because length of the support of the microscope is limited.
When observing different-size objects, the conventional microscope changes different objective lens to achieve zooming. This zooming microscope does not have auto-focusing function. Therefore, it needs to adjust the stage manually under a small magnification firstly to achieve correct focusing, and then to achieve zooming operation. This reduces work efficiency greatly. Furthermore, if the correct focusing is not done under the small magnification, then clear image cannot be formed in the subsequent zooming operation.
During the movement of the stage of the conventional microscope, the distance between the object and the microscope keeps changing and the amount of light transmission of the microscope changes too. The conventional microscope does not consider change of the amount of light transmission of the microscope. This causes overexposure or light lack of the image during the movement of the stage. The two situations will influence time and result of auto-focus of the microscope.